Puffer_freak said:
3g per litre, is that 3 grams per litre? What is the SG?
Also what are your readings for nitrIte and ammonia?
how long has the tank been established? Is it cycled? How big is the tank?
I also am not sure if puffers get dropsy.
"Dropsy
Symptoms
This disease is characterised by a swollen or hollow abdomen. Swollen areas may exhibit a 'pine-cone' appearance caused by the fishes scales sticking out. Fish may also appear off-colour and listless, and may stop feeding. The swelling caused by this disease may often be mistaken for a pregnant or egg-carrying fish. Gouramies and Cyprinids (barbs, danios, etc) are prone to this disease.
Causes
Dropsy is a condition with several possible causes. It may frequently be caused by internal infections by a number of different bacterial species. Viruses have also been associated with the disease. Poor water quality and/or diet may trigger the disease. If the problem has been caused by permanant damage to the kidney, then treating the infection will not eradicate the symptoms.
Possible cures
This disease must be caught early to maximise the chance of saving an affected fish, and even then the disease is difficult to cure. Previously, antibiotics prescribed by a vet were the only means of treatment for those countries (including the UK) where antibiotics cannot be purchased over-the-counter. There are now commercially available remedies which may help. These include Interpet #9 Anti Internal Bacteria and Waterlife's Octozin. The addition of salt (1 tsp/gallon) may also be beneficial.
Dropsy is not usually considered to be particularly contagious, so it should not spread to other healthy fish - dead fish should be removed immediately however, to avoid cannibalism. However, bear in mind that there is more than one cause of dropsy, so in some cases the infective agent could be contagious. It is preferable to carry out treatment in a hospital tank where available. "
The skin coming off does not sound like a symptom of dropsy, but it is diffiult to tell knowing little about diseases in puffers... the only disease I can find which refers to detached skin is slime disease:
"Slime Disease
This disease is also caused by protozoa e.g. Chilodonella, Ichthyobodo (Costia), Trichodina and Brooklynella species, and Trematodes (flukes) e.g. Gyrodactylus and Dactylogyrus species.
These parasites spend the whole of their life cycle on the fish, although infective young parasites may be released into the water to spread to new hosts. The parasites live on the skin and gill surface, eating gill and skin tissue debris. If their numbers increase rapidly, they may irritate the skin and gills, causing excessive mucus production and usually killing the fish by smothering the gills and hence suffocation. "
Hope thats some help...